The long term objectives of this research program are to elucidate the cortical contributions to spatial perception. The experiments of this proposal specifically address the cortical processing of visual, auditory, and combined visual and auditory stimuli in the primate. The visual system strongly modulates the perception of spatially and temporally disparate visual and auditory stimuli. Under some circumstances, for example when spatial and temporal disparities are small, visual stimuli are able to 'capture' the perceived location of auditory stimuli, giving rise to a unified percept of the multi-stimulus object. Under different circumstances, for example when the spatial and temporal disparities are large, the visual system is not able to capture the perceived location of the auditory stimulus, and therefore the percept is of two distinct objects. Although these perceptual illusions have been known and studied extensively, the neural basis of these perceptions is currently poorly understood. Neurons throughout the cerebral cortex and the superior colliculus have been described to respond to more than one stimulus modality. However, how these poly-sensory neurons contribute to spatial perception of multi-modal stimuli is also unclear. This is due largely to the lack of investigation of these neural responses with respect to the spatial perceptions elicited by them. A clearer understanding of how the different stimulus attributes of real world objects are integrated by the central nervous system, and ultimately process information that result in a unified percept of the real world, is critical to our understanding of the cortical mechanisms of sensory processing in general. These experiments will directly address the neuronal mechanisms of spatial perception of multi-modal stimuli by taking advantage of the interactions between visual and auditory stimuli in these perceptions. Single neuron activity will be defined under conditions where visual and auditory stimuli are simultaneously presented from the same location, as well as under conditions where the two stimulus modalities are disparate in space and/or time. These neuronal responses will be correlated with the resulting perception of the stimulus location. By using stimulus disparities that lead to both unified percepts of single bi-sensory objects, as well as perceptions of two distinct locations, a direct relationship between the neuronal activity and perception can be derived. These experiments will therefore directly address this fundamental process of sensory perception.